The unions have made it clear their preference is for the luxury brands to remain with Ford but in a surprise move backed Tata, despite the possibility that the Indian carmaker could move production abroad.

A statement from Unite, the UK's largest trade union, said that if a sale must be made, workers felt their best interests would be served by finding a partner with an established presence and background in manufacturing.

Tony Woodley, Unite joint general secretary, said the union shop stewards' decision was based on reports from presentations made by all the shortlisted bidders from the union representatives who attended.

Union shop stewards have reached this decision despite concerns that Tata might outsource production to India or change the brands' supply arrangements in the UK.

While union backing is not essential to either bidder, it could play an important political role in Ford's final decision.